1. Field of the Invention
The present invention relates to a scroll-type fluid machine used as a compressor or an expander.
This application is based on Patent Application No. Hei 9-311060 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
FIG. 3 shows an example of a conventional scroll-type fluid machine.
In the figure, reference numeral 1 indicates a housing comprising cup-like main body 2 and front housing 6 which is fastened to main body 2 using a bolt (not shown). Rotational shaft 7 which passes through the front housing 6 is supported by this front housing 6 via bearings 8 and 9, in a freely rotatable form.
Fixed scroll 10 and revolving scroll 14 are provided inside the housing 1. This fixed scroll 10 comprises end plate 11 and spiral lap 12 disposed on surface 11a of the plate 11, the surface facing end plate 15 explained later. The end plate 11 is fastened to cup-like main body 2 via bolt 13.
In the above structure, the outer-peripheral surface of the end plate 11 is in close contact with the inner-peripheral surface of the cup-like main body 2, and thereby internal partition of housing 1 is established in a manner such that discharge cavity 31 is limitedly provided outside the end plate 11, while suction chamber 28 is limitedly provided inside the end plate 11.
On the other hand, a central part of end plate 11 is bored to provide discharge port 29, and opening and closing operations of this discharge port 29 are performed using discharge valve 30. The rising motion of discharge valve 30 is restricted by valve presser 32, and one end of both discharge valve 30 and valve presser 32 are fastened to end plate 11 via bolt 33.
The revolving scroll 14 comprises end plate 15 and spiral lap 16 which is disposed on surface 15a of the plate 15, the surface facing the end plate 11. This spiral lap 16 has substantially the same shape as spiral lap 12 included in fixed scroll 10. The axes of the revolving and fixed scrolls 14 and 10 are eccentrically separated from each other by a predetermined distance, that is, they are in an eccentric form. In addition, phases of these scrolls are different from each other by 180.degree., and are engaged with each other as shown in FIG. 3.
Accordingly, tip seals 17, provided and buried at each head surface of spiral lap 12, are in close contact with surface 15a of end plate 15, while tip seals 18, provided and buried at each head surface of spiral lap 16, are in close contact with surface 11a of end plate 11. The side faces of spiral laps 12 and 16 have line contact at plural positions and thus plural compression chambers 19a and 19b are formed essentially at positions of point symmetry with respect to the center of the spiral.
Inside projecting disk-shaped boss 20, provided at a center area in the outer surface (opposite to inner surface 15a) of end plate 15, drive bush 21 is inserted in a freely rotatable form via revolving bearing 23. Slide groove 24 is cut into the drive bush 21, and eccentric drive pin 25 is inserted into the slide groove 24 so as to perform a sliding motion of the pin. The projecting drive pin 25 is eccentrically provided on an end face of larger-diameter portion 7a of rotational shaft 7, the portion 7a being provided on an end at the main body 2 side of the rotational shaft 7.
Between the peripheral edge of the outer surface of end plate 15 and an inner end face of front housing 6, thrust bearing 36 and Oldham link 26 are inserted. In order to balance a dynamically unbalanced situation due to a revolving motion of the revolving scroll 14, balance weight 27 is attached to drive bush 21, and balance weight 37 is attached to the rotational shaft 7.
According to the above structure, when the rotational shaft 7 is rotated, revolving scroll 14 is driven via a revolving-radius variable mechanism consisting of eccentric drive pin 25, slide groove 24, drive bush 21, revolving bearing 23, boss 20, etc. The revolving scroll 14 revolves along a circular orbit having a radius of revolution, while rotation of the scroll 14 is prohibited by the Oldham link 26.
In this way, the above-mentioned line-contact portions in the side faces of spiral laps 12 and 16 gradually move toward the center of "swirl", and thereby compression chambers 19a and 19b also move toward the center of the swirl while the volume of each chamber is gradually reduced.
Accordingly, gas, which has flowed into suction chamber 28 through an inlet (not shown), enters from an opening which is limitedly established by outer peripheral edges of spiral laps 12 and 16 to compression chambers 19a and 19b. This gas is gradually compressed and reaches central chamber 22. From the central chamber, the gas passes through discharge port 29, and presses and opens discharge valve 30, and thereby the gas is discharged into discharge cavity 31. The gas is then discharged outside via an outlet not shown.
At the time of operating the scroll-type compressor, when revolving scroll 14 revolves, balance weight 27 floats from the end face of larger-diameter portion 7a of the rotational shaft 7, and accordingly, drive bush 21 and revolving scroll 14 are inclined.
This inclination of revolving scroll 14 causes a situation in which the head or root portion of the side face of spiral lap 16 comes into partial contact with the side face of spiral lap 12 of fixed scroll 11. Therefore, not only abnormal abrasion between these sliding side faces is caused, but also volumetric efficiency of the scroll-type compressor is degraded due to leakage of gas from a gap generated between these sliding faces. In addition, slide portions such as thrust bearing 36, Oldham link 26, and revolving bearing 23 may not uniformly contact with an opposite portion in each relevant sliding motion, and thereby abnormal abrasion and seizure occur.
In consideration of the above situations, hole 38 is provided in balance weight 27 as shown in FIG. 2A, and the head of float-protecting pin 40, which passes through this hole 38 in a freely movable form, is pressed and fixed to hole 39 provided in larger-diameter portion 7a of rotational shaft 7. Regarding the back face of head 40a of this float-protecting pin 40, as shown in FIG. 2B, a portion of its peripheral area, existing at the opposite side to the drive bush 21, is in contact with an upper surface 27a of balance weight 27, so as to prevent the balance weight 27 from floating from the end face of the larger-diameter portion 7a of rotational shaft 7.
In the above-explained conventional scroll-type compressor, shaft 40b of the float-protecting pin 40 is fixed to the larger-diameter portion 7a of rotational shaft 7 and the head 40a of the pin has a circular shape of a predetermined diameter. Therefore, there occurs a problem in which restrictions are imposed on the structure, shape, size, and attachment position of the float-protecting pin 40.